Angiosperm Phylogeny Group
The Angiosperm Phylogeny Group (APG) is an informal international group of systematic botanists who collaborate to establish a consensus on the taxonomy of flowering plants (angiosperms) that reflects new knowledge about plant relationships discovered through phylogenetic studies.
As of 2016[update], four incremental versions of a classification system have resulted from this collaboration, published in 1998, 2003, 2009 and 2016. An important motivation for the group was what they considered deficiencies in prior angiosperm classifications since they were not based on
APG publications are increasingly influential, with a number of major herbaria changing the arrangement of their collections to match the latest APG system.
Angiosperm classification and the APG
In the past, classification systems were typically produced by an individual botanist or by a small group. The result was a large number of systems (see List of systems of plant taxonomy). Different systems and their updates were generally favoured in different countries. Examples are the Engler system in continental Europe, the Bentham & Hooker system in Britain (particularly influential because it was used by Kew), the Takhtajan system in the former Soviet Union and countries within its sphere of influence and the Cronquist system in the United States.[1]
Before the availability of genetic evidence, the classification of
After the 1980s, detailed genetic evidence analysed by
As of 2016[update], three revisions have been published, in 2003 (APG II), in 2009 (APG III) and in 2016 (APG IV), each superseding the previous system. Thirteen researchers have been listed as authors to the three papers, and a further 43 as contributors (see Members of the APG below).[5]
A classification presents a view at a particular point in time, based on a particular state of research. Independent researchers, including members of the APG, continue to publish their own views on areas of angiosperm taxonomy. Classifications change, however inconvenient this is to users. However, the APG publications are increasingly regarded as an authoritative point of reference and the following are some examples of the influence of the APG system:
- A significant number of major herbaria, including Kew, are changing the order of their collections in accordance with APG.[6]
- The influential World Checklist of Selected Plant Families (also from Kew) is being updated to the APG III system.[7]
- In the United States in 2006, a photographic survey of the plants of the US and Canada is organized according to the APG II system.[8]
- In the UK, the 2010 edition of the standard flora of the British Isles (by Stace) is based on the APG III system. The previous editions were based on the Cronquist system.[9]
Principles of the APG system
The principles of the APG's approach to classification were set out in the first paper of 1998, and have remained unchanged in subsequent revisions. Briefly, these are:[2]
- The Linnean system of orders and families should be retained. "The family is central in flowering plant systematics." An ordinal classification of families is proposed as a "reference tool of broad utility". Orders are considered to be of particular value in teaching and in studying family relationships.
- Groups should be phylogenetic.
- A broad approach is taken to defining the limits of groups such as orders and families. Thus of orders, it is said that a limited number of larger orders will be more useful. Families containing only a single genus and orders containing only a single family are avoided where this is possible without violating the over-riding requirement for monophyly.
- Above or parallel to the level of orders and families, the term clades is used more freely. (Some clades have later been given formal names in a paper associated with the 2009 revision of the APG system.[10]) The authors say that it is "not possible, nor is it desirable" to name all clades in a phylogenetic tree; however, systematists need to agree on names for some clades, particularly orders and families, to facilitate communication and discussion.
For a detailed discussion on phylogenetic nomenclature, see Cantino et al. (2007).[11])
APG I (1998)
The initial 1998 paper by the APG made angiosperms the first large group of organisms to be systematically re-classified primarily on the basis of genetic characteristics.
In 1998 only a handful of families had been adequately studied, but the primary aim was to obtain a consensus on the naming of higher orders. Such a consensus proved relatively easy to achieve but the resultant tree was highly unresolved. That is, while the relationship of orders was established, their composition was not.[12]
Other features of the proposed classification included:[citation needed]
- Formal, scientific names are not used above the level of order, named monocotsare not given a formal rank on the grounds that "it is not yet clear at which level they should be recognized".
- A substantial number of taxa whose classification had traditionally been uncertain are given places, although there still remain 25 families of "uncertain position".
- Alternative classifications are provided for some groups, in which a number of families can either be regarded as separate or can be merged into a single larger family. For example, the Fumariaceae can either be treated as a separate family or as part of Papaveraceae.
A major outcome of the classification was the disappearance of the traditional division of the flowering plants into two groups,
APG II (2003)
As the overall relationship between groups of flowering plants became clearer, the focus shifted to the family level, in particular those families generally accepted as problematic. Again, consensus was achieved relatively easily resulting in an updated classification at the family level.[12] The second paper published by the APG in 2003 presented an update to the original classification of 1998. The authors stated that changes were proposed only when there was "substantial new evidence" which supported them.[13]
The classification continued the tradition of seeking broad circumscriptions of taxa, for example trying to place small families containing only one genus in a larger group. The authors stated that they have generally accepted the views of specialists, although noting that specialists "nearly always favour splitting of groups" regarded as too varied in their morphology.[13]
APG II continued and indeed extends the use of alternative 'bracketed' taxa allowing the choice of either a large family or a number of smaller ones. For example, the large family Asparagaceae includes seven 'bracketed' families which can either be considered as part of the Asparagaceae or as separate families. Some of the main changes in APG II were:
- New orders are proposed, particularly to accommodate the 'basal clades' left as families in the first system.
- Many of the previously unplaced families are now located within the system.
- Several major families are re-structured.[13]
In 2007, a paper was published giving a linear ordering of the families in APG II, suitable for ordering herbarium specimens, for example.[14]
APG III (2009)
The third paper from the APG updates the system described in the 2003 paper. The broad outline of the system remains unchanged, but the number of previously unplaced families and genera is significantly reduced. This requires the recognition of both new orders and new families compared to the previous classification. The number of orders goes up from 45 to 59; only 10 families are not placed in an order and only two of these (
A major change is that the paper discontinues the use of 'bracketed' families in favour of larger, more inclusive families. As a result, the APG III system contains only 415 families, rather than the 457 of APG II. For example, the agave family (
In the same volume of the journal, two related papers were published. One gives a linear ordering of the families in APG III; as with the linear ordering published for APG II, this is intended for ordering herbarium specimens, for example.[17] The other paper gives, for the first time, a classification of the families in APG III which uses formal taxonomic ranks; previously only informal clade names were used above the ordinal level.[10]
APG IV (2016)
In the development of a fourth version there was some controversy over the methodology,
Further progress was made by the use of large banks of genes, including those of
Updates
Peter Stevens, one of the authors of all four of the APG papers, maintains a web site, the Angiosperm Phylogeny Website (APWeb), hosted by the Missouri Botanical Garden, which has been regularly updated since 2001, and is a useful source for the latest research in angiosperm phylogeny which follows the APG approach.[22] Other sources include the Angiosperm Phylogeny Poster[23] and The Flowering Plants Handbook.[24]
Members of the APG
Name | APG I | APG II | APG III | APG IV | Institutional affiliation |
---|---|---|---|---|---|
Birgitta Bremer | c | a | a | Swedish Academy of Sciences | |
Kåre Bremer | a | a | a | Uppsala University; Stockholm University | |
James W. Byng | a | Plant Gateway; University of Aberdeen | |||
Mark Wayne Chase | a | a | a | a | Royal Botanic Gardens, Kew |
Maarten J.M. Christenhusz | a | Plant Gateway; Royal Botanic Gardens, Kew | |||
Michael F. Fay
|
c | c | a | a | Royal Botanic Gardens, Kew |
Walter S. Judd | a | University of Florida | |||
David J. Mabberley | a | University of Oxford; Universiteit Leiden; Naturalis Biodiversity Center; Macquarie University; National Herbarium of New South Wales | |||
James L. Reveal | a | a | University of Maryland; Cornell University | ||
Alexander N. Sennikov | a | Finnish Museum of Natural History; Komarov Botanical Institute | |||
Douglas E. Soltis | c | a | a | a | University of Florida |
Pamela S. Soltis | c | a | a | a | Florida Museum of Natural History |
Peter F. Stevens | a | a | a | a | Harvard University Herbaria; University of Missouri-St. Louis and Missouri Botanical Garden |
a = listed as an author; c = listed as a contributor
References
- ^ a b Bhattacharyya & Bhattacharyya (2012)
- ^ a b c d e f APG I (1998)
- ^ Chase et al. (1993)
- ^ a b c d Fay (2016)
- ^ a b c Christenhusz et al. (2015)
- ^ a b c APG III (2009)
- ^ WCLSPF (2015)
- ^ Spears (2006)
- ^ Stace (2010)
- ^ a b Chase & Reveal (2009)
- ^ Cantino et al. (2007)
- ^ a b c d e APG IV (2016)
- ^ a b c APG II (2003)
- ^ Haston et al. (2007)
- ^ RBG (2009)
- ^ Wearn et al. (2013)
- ^ a b Haston et al. (2009)
- ^ Cole (2015)
- ^ Stevens (2015), On this classification in particular
- ^ Soltis et al. (2011)
- ^ Byng et al 2016.
- ^ Stevens (2015)
- ^ Cole et al 2019.
- ^ Byng (2014)
Bibliography
- Cantino, Philip D.; Doyle, James A.; Graham, Sean W.; JSTOR 25065865
- JSTOR 2399846
- ISBN 978-0-87893-817-9
- ISBN 9781139486491
- Maiti, Gaurgopal & Mukherjee, Sobhan Kr., eds. (2012), Multidisciplinary approaches in angiosperm systematics: XVIIIth Annual Conference of IAAT and International Seminar on 'Multidisciplinary Approaches in Angiosperm Systematics', held in the Department of Botany, University of Kalyani, Kalyani, Nadia, Kalyani, West Bengal: University of Kalyani, ISBN 978-93-5067-867-1, retrieved 31 August 2015
- Soltis, D. E.; Smith, S. A.; Cellinese, N.; Wurdack, K. J.; Tank, D. C.; Brockington, S. F.; Refulio-Rodriguez, N. F.; Walker, J. B.; Moore, M. J.; Carlsward, B. S.; Bell, C. D.; Latvis, M.; Crawley, S.; Black, C.; Diouf, D.; Xi, Z.; Rushworth, C. A.; Gitzendanner, M. A.; Sytsma, K. J.; Qiu, Y.-L.; Hilu, K. W.; Davis, C. C.; Sanderson, M. J.; Beaman, R. S.; Olmstead, R. G.; Judd, W. S.; Donoghue, M. J.; Soltis, P. S. (8 April 2011). "Angiosperm phylogeny: 17 genes, 640 taxa". American Journal of Botany. 98 (4): 704–730. PMID 21613169.
- Wearn, James A.;
- World Checklist of Selected Plant Families, Royal Botanic Gardens, Kew, retrieved 26 November 2015
APG
- Bhattacharyya, P.K. & Bhattacharyya, Kaustuv, "Comparison of the Angiosperm Phylogeny Group classification (2009) with that of the system of Takhtajan (2009) and a note on the Chase and Reveal (2009), Haston et al. (2009), and Mabberley (2008)", in Maiti & Mukherjee (2012), pp. 13–24
- . 181.
- Christenhusz, Maarten J.M.; Vorontsova, Maria S.;
- Haston, Elspeth; Richardson, James E.; Stevens, Peter F.; Chase, Mark W. & Harris, D.J. (2009), "The Linear Angiosperm Phylogeny Group (LAPG) III: a linear sequence of the families in APG III", Botanical Journal of the Linnean Society, 161 (2): 128–131,
- .
- Haston, E.; Richardson, J.E.; Stevens, P.F.; Chase, M.W. & Harris, D.J. (2007), "A linear sequence of Angiosperm Phylogeny Group II families", Taxon, 56 (1): 7–12
- Haston, Elspeth; Richardson, James E.; .
- Spears, Priscilla (2006), A tour of the flowering plants based on the classification system of the Angiosperm phylogeny group, St. Louis, Mo.: ISBN 978-1-930723-48-1
- Stevens, P.F. (2015) [1st. Pub. 2001], Angiosperm Phylogeny Website, retrieved 11 June 2016
- Cole, Theodor C.H. (2015), "Angiosperm Phylogeny Group (APG) in jeopardy – Where have the flowers gone?", PeerJ PrePrints: 3:e1517,
- Cole, Theodor C. H.; Hilger, Hartmut H.; , retrieved 29 November 2019
- Royal Botanic Gardens Kew. Retrieved 27 May 2019.
- "As easy as APG III - Scientists revise the system of classifying flowering plants", Kew News, Royal Botanic Gardens, Kew, 22 October 2009, archived from the original on 4 October 2015, retrieved 27 November 2015
- APG I-IV (1998–2016)
- Angiosperm Phylogeny Group (1998), "An ordinal classification for the families of flowering plants", JSTOR 2992015
- Angiosperm Phylogeny Group II (2003), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II" (PDF), doi:10.1046/j.1095-8339.2003.t01-1-00158.x, archived from the original(PDF) on 2020-10-22, retrieved 2019-09-24
- Angiosperm Phylogeny Group III (2009), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III", hdl:10654/18083
- Angiosperm Phylogeny Group IV (2016). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV". .